No abstract

Carcinoembryonic antigen (CEA, ceacam5) is an important tumor-associated antigen with reported roles, e.g., in immunological defense, cell adhesion, cell survival and metastasis. Its overexpression in cancer cells is known to involve transcriptional activation of the CEA gene, but the underlying molecular details remain unclear. Here, we show that hypoxia and intracellular alkalinization, 2 factors commonly found in solid tumors, increase CEA protein expression in breast (MCF-7) and colorectal (CaCo-2 and HT-29) cancer cells. The increase was comparable (2-3-fold) to that observed in colorectal carcinomas in vivo. CEA promoter analyses further revealed that this upregulation involves a known binding site for HIF-1 transcription factor (5 0 -ACGTG-3 0 ) within one of the CEA promoter's positive regulatory elements (the FP1 site; the E-box). Accordingly, deletion or targeted mutagenesis of this motif rendered the CEA promoter unresponsive to hypoxia. Our chromatin immunoprecipitation data confirmed that endogenous HIF-1a binds to the CEA promoter in hypoxic cells but not in normoxic cells. Moreover, overexpression of the hypoxia-inducible factor (HIF-1a) was sufficient to increase CEA protein expression in the cells. In contrast, c-Myc, which is known to bind to the overlapping E-box, did not potentiate HIF-1a-induced CEA expression. CEA overexpression in vivo was also found to coincide with the expression of carbonic anhydrase IX, a well-known hypoxia marker. Collectively, these results define CEA as a hypoxia-inducible protein and suggest an important role for the tumor microenvironmental factors in CEA overexpression during tumorigenesis. ' 2007 Wiley-Liss, Inc.Key words: neoplasia; carcinoembryonic antigen expression; hypoxia; pH homeostasis Carcinoembryonic antigen (CEA, ceacam5), originally identified about 40 years ago, 1 is a widely used tumor marker and also currently a target for vaccine-based immunotherapy. 2,3 It is a 180-200 kDa glycoprotein attached to the apical membrane of epithelial cells via its C-terminal glycosylphosphatidylinositol (GPI) anchor. It has been assigned multiple functions, including a role in immunological defense, cell signaling and cell adhesion. When overexpressed, it has also been shown to inhibit apoptosis, anoikis, cell polarity and differentiation, 3-9 and to promote anchorage-independent growth and tumor formation in nude mice. 10 CEA expression commences during the early fetal life and continues thereafter at low levels mainly in the epithelial cells of the gastrointestinal tract, cervix, sweat glands and the prostate. 3 It is re-expressed at higher levels (2-6-fold) in many cancers. 2,11,12 Previous studies 13 have shown that this upregulation does not involve gene amplification nor its rearrangements. Rather, CEA protein levels were found to correlate with its mRNA levels in the cells and tissues examined, suggesting that CEA overexpression in cancer cells involves transcriptional activation of the CEA gene. However, the underlying molecular details have remained uncle...

Dyxin is a novel LIM domain protein acting as a transcriptional cofactor with GATA transcription factors. Here, we characterized dyxin as a p38 mitogen-activated protein kinase (MAPK) regulated gene, since combined upstream MAPK kinase 3b and wild-type p38 alpha MAPK gene transfer increased left ventricular dyxin mRNA and protein levels in vivo. We also studied cardiac dyxin expression in experimental models of pressure overload and myocardial infarction (MI) in vivo. Angiotensin II infusion increased left ventricular dyxin mRNA levels (9.4-fold, p<0.001) rapidly at 6 h followed by induction of protein levels. Furthermore, simultaneous administration of p38 MAPK inhibitor SB203580 abolished angiotensin II-induced activation of dyxin gene expression. During the post-infarction remodeling process, increased dyxin mRNA levels (7.7-fold, p<0.01) were noted at day 1 followed by the increase in proteins levels at 2 weeks after MI (1.5-fold, p<0.05). Moreover, direct wall stretch by using isolated rat heart preparation as well as direct mechanical stretch of cardiomyocytes in vitro activated dyxin gene expression within 1 h. Our results indicate that dyxin expression is rapidly upregulated in response to mechanical load, this increase being at least partly mediated by p38 MAPK. These results suggest that dyxin may play an important role in regulating hypertrophic process.